There are molecules that cannot be represented by a single structure. Although it is possible to run multiple structure searches in cascade, it is much more efficient to run a search only once using a well designed query structure. This structure often contains query features, possibly including complex conditional expressions for atoms and bonds. For a more detailed description of this please see the Query Guide.
The easiest way to use Query Atoms, different Query Groups and Query Atom Properties is to find them on the Periodic Table's Advanced tab.